The present invention relates generally to scintillation cameras, commonly called gamma cameras, and is particularly concerned with the configuration of a suspended arm for supporting a detector head of the camera.
In a diagnostic nuclear medicine, scintillation camera systems are used to detect gamma ray photons emitted from a body in which a radioisotope has been infused. Scintillations occur where photons are absorbed by crystalline material. A typical system is based on the camera of Anger, as disclosed in U.S. Pat. No. 3,011,057. As in the Anger camera, the camera detector head disclosed herein comprises an array of photosensitive devices, such as photomultiplier tubes, having their input ends adjacent to a light plate or disk. Beneath the disk is a scintillation crystal which converts incoming gamma photons into light photons or scintillations. A collimator is interposed between the scintillator and the emitting body so that the emitted photons will impinge substantially perpendicularly to the planer scintillation crystal. The photomultiplier tubes produce a pulse for each scintillation event. Well known electronic circuits are used to produce signals representing the x and y coordinates of the scintillations. A signal is produced which controls a cathode ray oscilloscope display to produce a point of light on its screen at the x and y coordinates corresponding with those of the scintillation event intercepted by the camera. A photographic film may be used as an image integrator of the large number of light spots appearing on the screen on the cathode ray tube. A substantial number of events is required to make up the final picture of radioisotope distribution in the body tissue.
A scintillation camera is commonly mounted as a portable unit which can readily be moved to a patient's bed or other location where a study is to be conducted. The detector head is supported in cantilevered fashion over the patient to be studied. The detector head is movable manually to a desired position.
A particular problem with scintillation cameras of the prior art is illustrated in FIG. 1. The cantilevered support arm extends horizontally from a suspension system to the detector head. It is often desired to image a portion of the far side of the patient. It is readily shown that if the detector head is extended over the patient and lowered for imaging a portion of the far side of the patient, the suspended arm would interfere with the body of the patient (as shown by the hashed lines). It was, therefore, necessary to interrupt the analysis to reposition the camera or the patient in order to image the desired area. This problem was particularly apparent during cardiac analysis where immediately successive images of the right anterior oblique view, vertical view and the left anterior oblique view of the heart are required for proper analysis of cardiac performance.
Another problem with the suspended arm of the prior art was the limited extension and restricted freedom of position of the arm and the detector head. A pair of rigid, horizontal arms were typically provided to position the detector head. The arms had internally telescoping members which provided limited extension and had a pivot for radial positioning. It was frequently necessary to reposition either the patient or the base of the camera for imaging the desired locations of the patient during analysis.
Accordingly, one object of the present invention is to provide a suspended arm for a scintillation camera which can be readily manipulated to position the detector head in desired locations for imaging a patient.
Another object of the present invention is to provide a suspended arm for a scintillation camera which can be manually positioned and readily locked to retain that desired position during analysis of a patient.